The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, HDDs have been desired to store more information in its limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
The further miniaturization of the various components, however, presents its own set of challenges and obstacles. In discrete track media (DTM) and/or bit-patterned media (BPM), the variation in track pitch arises at the time of manufacture. In a magnetic data storage device, such as a HDD, position information indicating the position of the magnetic head over the medium is written on the surface thereof at constant circumferential intervals (this information is typically referred to as “servo information” and the regions containing this information are referred to as “servo sectors”), and a plurality of concentric tracks (track numbers 1 to Tn (where Tn is an integer)) are formed in which each circumference constitutes one track. The servo information is written on the magnetic disk medium using a dedicated servo track writer, self-servo write, or some other technique. Furthermore, in each track, the area from a certain servo sector to the following servo sector is allocated as a region for writing data (this is typically referred to as a data sector). Various kinds of information are written in the data sector using the magnetic disk device. That is, sectors wherein the minimum unit is a set comprising one servo sector and one data sector are continuously formed over each track.
The magnetic disk recorded in the device reads the position information servo sectors on the magnetic disk medium using a magnetic head, and a servo motor for positioning the magnetic head in the radial direction of the magnetic disk medium performs rotation control based on the difference from the read position thereof to the target position, whereby the magnetic head is made to reach the target position.
A continuous thin-film medium is conventionally used for the magnetic disk medium. Data is written to the continuous thin-film medium on which the servo information is recorded by moving the magnetic head to the servo sector belonging to the track number designated for data writing scanning the magnetic disk medium from that servo sector to a servo sector having a designated sector number by rotating the magnetic disk medium, and then generating a writing magnetic field using the magnetic head, from the latter stage of the designated servo sector to the following servo sector. It should be noted that the servo information in each servo sector contains burst information as correction information for each servo sector in order for the magnetic head to reach the center of the following servo sector, and the magnetic head reads out the correction information at each servo sector and performs fine adjustments to the position of arrival in the following servo sector so as to suppress positional offset in that servo sector. Furthermore, when data is read out, the magnetic head scans on the above track over the data sectors where data is written by the magnetic head on the same track, and the data which is magnetically written is reproduced from the magnetic head as electrical signals.
In the continuous thin-film medium, the servo sectors are formed by a servo track writer, etc., but the data sectors are formed without further processing on the movement path of the magnetic head which passes through the servo sectors under the above mentioned positional control, and the path thereof forms the tracks of the magnetic disk medium. This path will is typically referred to as the servo path, the servo sector portion within the tracks thereof is referred to as servo tracks, and the data sector portion is referred to as data tracks.
As described above, the servo sector information is recorded on the magnetic disk medium by a servo track writer. This involves processing which is carried out before product shipment, and therefore if the magnetic disk medium is formed before the device is actually shipped, a certain amount of variation will be produced in the positioning accuracy of the magnetic head in the servo sectors depending on the devices in which the magnetic disk medium has been installed. Consequently, the user suppresses the occurrence of positional offset of the magnetic head in the servo sector position by writing position correction information for suppressing variations in the device to a user writable region, referred to as an repeatable run-out (RRO) region, which is provided in the servo sectors.
For this reason, in order to make the write head on track, RRO should be rectified. However, conventional methods of measuring track pitch for each and every track of the media is not realistic.